“Dozens of human embryos with three parents have been created by British scientists,” reported the Daily Mail. Many papers covered this experimental technique aimed at preventing genetic disorders.
The technique, which has previously been tested in monkeys, results in embryos that have nuclear DNA from both parents and donor mitochondria from another woman. The embryos were destroyed after eight days of growth. Mitochondria are often referred to as the "batteries" of cells as they produce energy. Mutations in mitochondrial DNA cause at least 150 hereditary conditions.
This technique could potentially be used to help women with severe mitochondrial mutations to have children without these mutations. As mitochondrial DNA only makes up a very small part of the total DNA in cells, the offspring's characteristics would still mostly be derived from the nuclear DNA of the mother and father.
Several newspapers claim that this technique has similarities with cloning. This is not the case however and the technique is similar to types of IVF already in use. It does involve making genetic changes to unborn children who will have some DNA from two mothers, and the ethical issues of future research into this technique will need to be considered by the Human Embryology and Fertilisation Authority.
Where did the story come from?
The research was carried out by Dr Lyndsey Craven and colleagues from the Mitochondrial Research Group at the Institute for Ageing and Health in Newcastle University. The study received funding from several sources including the Muscular Dystrophy Campaign, the Wellcome Trust and the Medical Research Council. It was published in the peer-reviewed journal Nature.
The media covered the story in some depth, accurately reporting the technique, with diagrams in some cases, and the related ethical issues. However, some reports may have given readers the impression that the research is at a later stage of development than it is. The researchers estimate that the technique is three years away from being tested in trials for these conditions.
What kind of research was this?
This laboratory study investigated whether pronuclear transfer (transfer of DNA from the nucleus of one egg to another) in human embryos is possible and, if so, what proportion of embryos survive for six to eight days and how much donor mitochondrial DNA is carried over to the new embryo.
The study was appropriately designed to answer these questions. Researchers are currently prohibited from allowing embryos, such as the ones in this study, to develop beyond six to eight days and from implanting them back into the womb. For this technique to progress further, appropriate ethics approval and a change in the law would be necessary.
What did the research involve?
The researchers explain that mutations in mitochondrial DNA are a common cause of genetic disease, responsible for at least 150 hereditary conditions. Mitochondria are present in all cells and are often referred to as the cells’ “batteries” as they produce energy. They are found in the membrane-bound structures that lie outside the nucleus. The nucleus is where most DNA is found, but mitochondria have some DNA of their own.
Mitochondrial DNA mutations can result in neurological, muscular and heart problems and deafness. Some of these conditions are serious and can be fatal at birth. Around 1 child in 6,500 is born with a mitochondrial disease, and at least 1 adult in every 10,000 is affected by disease caused by mutations in their mitochondrial DNA. As each cell has multiple mitochondria, whether or not a person is affected by a mitochondrial disease depends on the proportion of their mitochondria that carry the mutation. Disease occurs in people carrying the mutation in at least 60% of their mitochondria.
The study used abnormally fertilised one-cell embryos (called zygotes), which had been donated by patients having IVF treatment at the Newcastle Fertility Centre. These eggs are usually not used in fertility treatment as they are not normal and typically do not survive. These abnormally fertilised eggs were identified at day one of their development at the Fertility Centre.
The researchers took the nucleus together with some plasma membrane and a small amount of the surrounding cytoplasm out of the cell and transferred it to an empty recipient cell. The recipient cell was also an abnormally fertilised zygote, at the same stage as the donor’s cell. This cell had had its nuclear DNA removed, using a similar process to that used on the donor cell. After the nucleus from the first embryo had been inserted into the recipient cell, it was either cultured for six to eight days to monitor development or cultured for a short period before being analysed for its mitochondrial DNA content.
Accepted genotyping techniques were used to determine the carry-over of mitochondrial DNA from the donor zygote into the recipient cell. This is important because, if the technique were to be used to prevent mitochondrial mutation disease in humans, it would need to be known how much, if any, mutated mitochondrial DNA is transferred along with the nucleus.
What were the basic results?
The researchers report that the transfer of the nucleus was successful. There was minimal carry-over of donor zygote mitochondrial DNA into the recipient cell (less than 2% after improving the procedure). Many of these early embryos contained no detectable donor mitochondrial DNA. The researchers say that this technique would allow onward development to embryo stage.
How did the researchers interpret the results?
The researchers concluded that pronuclear transfer between zygotes has the “potential to prevent the transmission of mitochondrial DNA disease in humans”.
Conclusion
Current treatments, including genetic counselling and pre-implantation genetic diagnosis, can help women who have only low levels of mutations in the mitochondria of their egg cells to have children of their own. This new technique could potentially help women who have more mutations and who may otherwise not be able to have children.
It is important to note that the third parent (the donor of the recipient egg) in the news reports only supplied a small, but essential, part of the genetic code for these embryos. This DNA affects energy production in cells and would probably not affect the offspring’s characteristics in a noticeable way.
There are further ethical and research obstacles to overcome before the technique could be available to affected families. First, an ethical debate about the procedure will need to occur. Second, how the procedure is regulated, if it is approved, will need to be agreed. Long-term safety of the procedure and refinements in the technique would also need be looked at in a research setting.
Tuesday, April 5, 2011
Defective DNA Repair and Neurodegenerative Disease
Defects in cellular DNA repair processes have been linked to genome instability, heritable cancers, and premature aging syndromes. Yet defects in some repair processes manifest themselves primarily in neuronal tissues. This review focuses on studies defining the molecular defects associated with several human neurological disorders, particularly ataxia with oculomotor apraxia 1 (AOA1) and spinocerebellar ataxia with axonal neuropathy 1 (SCAN1). A picture is emerging to suggest that brain cells, due to their nonproliferative nature, may be particularly prone to the progressive accumulation of unrepaired DNA lesions.
DNA chips detect disease
A DNA chip that can identify genetic mutations has been synthesised by Japanese scientists.
The most common form of genetic variation between individuals is caused by single-nucleotide differences in our DNA code. These are called single nucleotide polymorphisms (SNPs). SNPs can be used to identify disease genes and can highlight when a person is likely to develop a disease.
Kenzo Fujimoto and colleagues at the Japan Advanced Institute of Science and Technology have developed a simple and rapid method for identifying SNPs. The method could be the basis for automated, high-throughput diagnosis, they claim.
The method uses a short strand of DNA, known as an oligodeoxynucleotide probe, attached to a glass chip. The probe contains DNA bases complementary to those in the DNA strand containing the SNP of interest, except that one base is replaced by a vinyl-containing nucleoside known as cvP. When Fujimoto placed the target DNA onto the chip and shone ultraviolet light on it, the cvP reacted with an adenine base on the target DNA, in a reaction known as photocrosslinking. Fujimoto detected the photocrosslinked product using fluorescence imaging.
Because photocrosslinking only occurs when all the bases on the probe are complementary to those on the target DNA, if there is a mismatch in the strands the chip does not fluoresce.
'This method is an efficient reaction and proceeds with high sequence specificity,' said Fujimoto. 'Photochemical DNA manipulation is a highly original research theme.'
Hans-Achim Wagenknecht, an expert in molecular diagnostics at the University of Regensburg, Germany, believes the work represents a significant improvement for SNP detection. 'Such cheap, sensitive and reliable screening tools are clearly needed for the clinical diagnostics of genetic variations, infectious diseases and pharmacology,' he said.
The most common form of genetic variation between individuals is caused by single-nucleotide differences in our DNA code. These are called single nucleotide polymorphisms (SNPs). SNPs can be used to identify disease genes and can highlight when a person is likely to develop a disease.
Kenzo Fujimoto and colleagues at the Japan Advanced Institute of Science and Technology have developed a simple and rapid method for identifying SNPs. The method could be the basis for automated, high-throughput diagnosis, they claim.
The method uses a short strand of DNA, known as an oligodeoxynucleotide probe, attached to a glass chip. The probe contains DNA bases complementary to those in the DNA strand containing the SNP of interest, except that one base is replaced by a vinyl-containing nucleoside known as cvP. When Fujimoto placed the target DNA onto the chip and shone ultraviolet light on it, the cvP reacted with an adenine base on the target DNA, in a reaction known as photocrosslinking. Fujimoto detected the photocrosslinked product using fluorescence imaging.
Because photocrosslinking only occurs when all the bases on the probe are complementary to those on the target DNA, if there is a mismatch in the strands the chip does not fluoresce.
'This method is an efficient reaction and proceeds with high sequence specificity,' said Fujimoto. 'Photochemical DNA manipulation is a highly original research theme.'
Hans-Achim Wagenknecht, an expert in molecular diagnostics at the University of Regensburg, Germany, believes the work represents a significant improvement for SNP detection. 'Such cheap, sensitive and reliable screening tools are clearly needed for the clinical diagnostics of genetic variations, infectious diseases and pharmacology,' he said.
From DNA Data to Disease Diagnosis
What kind of information is used in association studies, and what answers can be obtained from them?
In a typical disease association study, a researcher collects DNA samples from a population of controls, or healthy individuals, and from a population of cases, who are individuals carrying the disease. The idea of such studies is that now we can search for differences in the DNA composition between the cases and the controls; such differences serve as an evidence for a relation between the disease and a genetic variant, which is a part of the DNA that varies across the population.
Due to the high cost of DNA sequencing, it is currently impossible to compare the entire DNA sequence across the set of individuals participating in the study; in a typical study there are thousands of cases and controls, and the cost of sequencing the entire genome of a single individual is still in the order of tens of thousands of dollars. For this reason, typically one will consider genetic variants that are common in the population. The most common variants are called Single Nucleotide Polymorphisms (SNPs), which are nucleotide base positions in the genome that differ across the population. Thus, if A,G,C, and T represent the four building blocks of the DNA, then for example in a SNP position you may find that 20% of the population carry the ‘A’ version and 80% carry the ‘C’ version. It is estimated that there are about 10 million SNPs in the genome, and in the other positions in the genome all individuals have the same DNA.
In a typical disease association study about 1 million SNPs are sampled per individual; we then search for differences between the frequencies of the SNPs in the cases and the controls. Once we discover such association we can further explore the reason for the association using ‘functional studies’ in which the specific genes are studied in the context of the disease. Furthermore, we can use the results of the genome-wide association studies to estimate the risk of an individual to develop a disease.
Where is this information obtained from? Are there specific, widely used processes for public and private researchers to obtain access to it?
The information is obtained in the lab, and is kept privately there, in order to protect the privacy of the study participants. In order to be able to share this information among scientists, there are databases maintained by the National Institute of Health in which the data is deposited and scientists can access the data if they need to use it for their research and if they prove that they can protect the privacy and rights of the study’s participants.
In a typical disease association study, a researcher collects DNA samples from a population of controls, or healthy individuals, and from a population of cases, who are individuals carrying the disease. The idea of such studies is that now we can search for differences in the DNA composition between the cases and the controls; such differences serve as an evidence for a relation between the disease and a genetic variant, which is a part of the DNA that varies across the population.
Due to the high cost of DNA sequencing, it is currently impossible to compare the entire DNA sequence across the set of individuals participating in the study; in a typical study there are thousands of cases and controls, and the cost of sequencing the entire genome of a single individual is still in the order of tens of thousands of dollars. For this reason, typically one will consider genetic variants that are common in the population. The most common variants are called Single Nucleotide Polymorphisms (SNPs), which are nucleotide base positions in the genome that differ across the population. Thus, if A,G,C, and T represent the four building blocks of the DNA, then for example in a SNP position you may find that 20% of the population carry the ‘A’ version and 80% carry the ‘C’ version. It is estimated that there are about 10 million SNPs in the genome, and in the other positions in the genome all individuals have the same DNA.
In a typical disease association study about 1 million SNPs are sampled per individual; we then search for differences between the frequencies of the SNPs in the cases and the controls. Once we discover such association we can further explore the reason for the association using ‘functional studies’ in which the specific genes are studied in the context of the disease. Furthermore, we can use the results of the genome-wide association studies to estimate the risk of an individual to develop a disease.
Where is this information obtained from? Are there specific, widely used processes for public and private researchers to obtain access to it?
The information is obtained in the lab, and is kept privately there, in order to protect the privacy of the study participants. In order to be able to share this information among scientists, there are databases maintained by the National Institute of Health in which the data is deposited and scientists can access the data if they need to use it for their research and if they prove that they can protect the privacy and rights of the study’s participants.
UNP and DNA to join hands to release Fonseka in Sri Lanka
The UNP and Democratic National Alliance (DNA) are likely to join hands and form an alliance once again to free former army commander Sarath Fonseka who is now imprisoned in Welikada.
The UNP has invited the DNA to join their protest campaign to free Fonseka who was sentenced last Friday to 30 months in jail. UNP General Secretary Tissa Attanayake told LAKBIMAnEWS that they have already sent out an invitation calling on the DNA to join them in their bid to release Fonseka.
The UNP and the JVP, for the first time in their political history joined hands during the last presidential election to work together to campaign for Fonseka s victory.
We believe that it s better to conduct the protests together because we can then create a bigger impact. This is the time that all political parties and civil society organizations should come together to free Fonseka who has been wrongfully imprisoned, he said.
UNP leader Ranil Wickremesinghe is scheduled to meet political parties and various organizations this week to come to a final agreement.
Attanayake added that they refuse to accept the court martial decision and they have already complained to the Human Rights Council in Geneva. Gampaha District parliamentarian, Dr. Jayalath Jayawardana is currently in Geneva to do the necessary spadework he added.
We have organized a series of religious ceremonies with the participation of all religious leaders which will commence at Pugoda from October, 3. We need to gather all those who are against this regime, he said.
Meanwhile the DNA has not yet taken a final decision about forming a formal alliance with the UNP, DNA General Secretary MP Vijitha Herath told LAKBIMAnEWS.
He added that their campaign is open to anyone and that the DNA launched its protest campaign demanding Fonseka s release in Kadawatha yesterday. Police have been meanwhile deployed to sabotage their poster campaign to protest Fonseka s arrest. Several JVPers who were putting up posters have been taken into custody at several places and in certain areas posters have even been torn by police personnel, Herath said.
The UNP has invited the DNA to join their protest campaign to free Fonseka who was sentenced last Friday to 30 months in jail. UNP General Secretary Tissa Attanayake told LAKBIMAnEWS that they have already sent out an invitation calling on the DNA to join them in their bid to release Fonseka.
The UNP and the JVP, for the first time in their political history joined hands during the last presidential election to work together to campaign for Fonseka s victory.
We believe that it s better to conduct the protests together because we can then create a bigger impact. This is the time that all political parties and civil society organizations should come together to free Fonseka who has been wrongfully imprisoned, he said.
UNP leader Ranil Wickremesinghe is scheduled to meet political parties and various organizations this week to come to a final agreement.
Attanayake added that they refuse to accept the court martial decision and they have already complained to the Human Rights Council in Geneva. Gampaha District parliamentarian, Dr. Jayalath Jayawardana is currently in Geneva to do the necessary spadework he added.
We have organized a series of religious ceremonies with the participation of all religious leaders which will commence at Pugoda from October, 3. We need to gather all those who are against this regime, he said.
Meanwhile the DNA has not yet taken a final decision about forming a formal alliance with the UNP, DNA General Secretary MP Vijitha Herath told LAKBIMAnEWS.
He added that their campaign is open to anyone and that the DNA launched its protest campaign demanding Fonseka s release in Kadawatha yesterday. Police have been meanwhile deployed to sabotage their poster campaign to protest Fonseka s arrest. Several JVPers who were putting up posters have been taken into custody at several places and in certain areas posters have even been torn by police personnel, Herath said.
Friday, March 11, 2011
Unanswered Questions and Inherent Uncertainties
What's wrong with Genetic Engineering ?
Genetic Engineering is a test tube science and is prematurely applied in food production. A gene studied in a test tube can only tell what this gene does and how it behaves in that particular test tube. It cannot tell us what its role and behaviour are in the organism it came from or what it might do if we place it into a completely different species. Genes for the colour red placed into petunia flowers not only changed the colour of the petals but also decreased fertility and altered the growth of
the roots and leaves. Salmon genetically engineered with a growth hormone gene not only grew too big too fast but also turned green. These are unpredictable side effects, scientifically termed pleiotropic effects.
We also know very little about what a gene (or for that matter any of its DNA sequence) might trigger or interrupt depending on where it got inserted into the new host (plant or animal). These are open questions around positional effects. And what about gene silencing and gene instability? How do we know that a genetically engineered food plant will not produce new toxins and allergenic substances or increase the level of dormant toxins and allergens? How about the nutritional value? And what are the effects on the environment and on wild life? All these questions are important questions yet they remain unanswered. Until we have an answer to all of these, genetic engineering should be kept to the test tubes. Biotechnology married to corporations tends to ignore the precautionary principle but it also igpores some basic scientific principles.
What you can do:
þ Avoid genetically engineered (GE) food, currently in products containing soya and maize.
þ Buy organic products - look for the Soil Association label.
þ Tell your MP and the Minister of the Environment you object to GE crops being released on test sites in your area -or any area you care about. Ask your MP or the Department of Environment, Transport and the Regions (DETR) for details from the Public Register of GMOs (genetically modified organisms). DETR phone: 0171-890 5275.
þ Copy this briefing and give it to a neighbour /friend.
þ Contact your local paper; write a letter to the editor.
þ Demand clear choice and non-GE products from your supermarket (addresses of head offices and sample letter available from WEN).
þ Read up on the issue. Get WEN's Campaign Pack on Genetic Engineering (out in August, L2).
þ Join a local environmental group and campaign against GE crops and GE food.
þ Support WEN's Test Tube Harvest Campaign (cheques payable to: 'WEN- Test Tube Harvest').
þ Join the Women's Environmental Network.
þ Contact the Test Tube Harvest Campaign for further information.
Genetic Engineering is a test tube science and is prematurely applied in food production. A gene studied in a test tube can only tell what this gene does and how it behaves in that particular test tube. It cannot tell us what its role and behaviour are in the organism it came from or what it might do if we place it into a completely different species. Genes for the colour red placed into petunia flowers not only changed the colour of the petals but also decreased fertility and altered the growth of
the roots and leaves. Salmon genetically engineered with a growth hormone gene not only grew too big too fast but also turned green. These are unpredictable side effects, scientifically termed pleiotropic effects.
We also know very little about what a gene (or for that matter any of its DNA sequence) might trigger or interrupt depending on where it got inserted into the new host (plant or animal). These are open questions around positional effects. And what about gene silencing and gene instability? How do we know that a genetically engineered food plant will not produce new toxins and allergenic substances or increase the level of dormant toxins and allergens? How about the nutritional value? And what are the effects on the environment and on wild life? All these questions are important questions yet they remain unanswered. Until we have an answer to all of these, genetic engineering should be kept to the test tubes. Biotechnology married to corporations tends to ignore the precautionary principle but it also igpores some basic scientific principles.
What you can do:
þ Avoid genetically engineered (GE) food, currently in products containing soya and maize.
þ Buy organic products - look for the Soil Association label.
þ Tell your MP and the Minister of the Environment you object to GE crops being released on test sites in your area -or any area you care about. Ask your MP or the Department of Environment, Transport and the Regions (DETR) for details from the Public Register of GMOs (genetically modified organisms). DETR phone: 0171-890 5275.
þ Copy this briefing and give it to a neighbour /friend.
þ Contact your local paper; write a letter to the editor.
þ Demand clear choice and non-GE products from your supermarket (addresses of head offices and sample letter available from WEN).
þ Read up on the issue. Get WEN's Campaign Pack on Genetic Engineering (out in August, L2).
þ Join a local environmental group and campaign against GE crops and GE food.
þ Support WEN's Test Tube Harvest Campaign (cheques payable to: 'WEN- Test Tube Harvest').
þ Join the Women's Environmental Network.
þ Contact the Test Tube Harvest Campaign for further information.
Working with plasmids.
Plasmids are relatively small, replicate very quickly and are thus easy to study and to manipulate. It is easy to determine the sequence of its DNA, that is, to find out the sequence of the letters (A, C, G and 1) and number them. Certain letter combinations -such as CAATTG - are easy to cut with the help of specific enzymes (see proteins). Ilese cutting enzymes, called restriction enzymes, are part of the Genetic Engineering "tool-kit" of biochemists. So if I want to splice a gene from fish into a plasmid, I have to take the following steps: I place a large number of a known plasmid in a little test tube and add a specific enzyme that will cut the plasmid at only one site. After an hour I stop the digest, purify the cut plasmid DNA and mix it with copies of the fish gene; after some time the fish gene places itself into the cut ring of the plasmid. I quickly add some "glue" from my "tool-kit" - an enzyme called ligase - and place the mended plasmids back into bacteria, leaving them to grow and multiply. But how do I know which bacteria will have my precious plasmid? For this reason I need MARKER GENES, such as antibiotic resistance genes. So I make sure my plasmid has a marker gene before I splice my fish gene into it. If thA I plasmid is marked with a gene antibiotic resistance I can now add specific antibiotic to the food supply of the bacteria. All those which do not have the plasmid will die, and all those that do have the plasmid will multiply.
What is a plasmid?
PLASMIDS can be found in many bacteria and are small rings of DNA with a limited number of genes. Plasmids are not essential for the survival of bacteria but can make life a lot easier for them. Whilst all bacteria - no matter which species - will have their bacterial chromosome with all the crucial hereditary information of how to survive and multiply, they invented a tool to exchange information rapidly. If one likens the chromosome to a bookshelf with manuals and handbooks, and a single gene to a recipe or a specific building instruction, a plasmid,could be seen as a pamphlet. Plasmids self-replicate and are thus easily reproduced and passed around. Plasmids often contain genes for antibiotic resistance. This type of information which can easily be passed on, can be crucial to bacterial strains which are under attack by drugs and is indeed a major reason for the quick spread of antibiotic resistance.
How to get the gene into the other cell.
There are different ways to get a gene from A to B or to transform a plant with a "new" gene. A VECTOR is something that can carry the gene into the host, or rather into the nucleus of a host cell. Vectors are commonly bacterial plasmids (see below and next page) or viruses (a). Another method is the "SHOTGUN TECHNIQUE" also known as "bio-ballistics," which blindly shoots masses of tiny gold particles coated with the gene into a plate of plant cells, hoping to land a hit somewhere in the cell's DNA (b).
Genetic Engineering.
Genetic engineering (GE) is used to take genes and segments of DNA from one species, e.g. fish, and put them into another species, e.g. tomato. To do so, GE provides a set of techniques to cut DNA either randomly or at a number of specific sites. Once isolated one can study the different segments of DNA, multiply them up and splice them (stick them) next to any other DNA of another cell or organism. GE makes it possible to break through the species barrier and to shuffle information between completely unrelated species; for example, to splice the anti-freeze gene from flounder into tomatoes or strawberries, an insect-killing toxin gene from bacteria into maize, cotton or rape seed, or genes from humans into pig.
Yet there is a problem - a fish gene will not work in tomato unless I give it a promoter with a "flag" the tomato cells will recognise. Such a control sequence should either be a tomato sequence or something similar. Most companies and scientists do a shortcut here and don't even bother to look for an appropriate tomato promoter as it would take years to understand how the cell's internal communication and regulation works. In order to avoid long testing and adjusting, most genetic engineering of plants is done with viral promoters. Viruses - as you will be aware - are very active. Nothing, or almost nothing, will stop them once they have found a new victim or rather host. They integrate their genetic information into the DNA of a host cell (such as one of your own), multiply, infect the next cells and multiply. This is possible because viruses have evolved very powerful promoters which command the host cell to constantly read the viral genes and produce viral proteins. Simply by taking a control element (promoter) from a plant virus and sticking it in front of the information block of the fish gene, you can get this combined virus/fish gene (known as a "construct') to work wherever and whenever you want in a plant.
This might sound great, the drawback though is that it can't be stopped either, it can't be switched off. The plant no longer has a say in the expression of the new gene, even when the constant involuntary production of the "new" product is weakening the plant's defences or growth.
And furthermore, the theory doesn't hold up with reality. Often, for no apparent reason, the new gene only works for a limited amount of time and then "falls silent". But there is no way to know in advance if this will happen.
Though often hailed as a precise method, the final stage of placing the new gene into a receiving higher organism is rather crude, seriously lacking both precision and predictability. The "new" gene can end up anywhere, next to any
gene or even within another gene, disturbing its function or regulation. If the "new" gene gets into the "quiet" non-expressed areas of the cell's DNA, it is likely to interfere with the regulation of gene expression of the whole region. It could potentially cause genes in the "quiet" DNA to become active.
Often genetic engineering will not only use the information of one gene and put it behind the promoter of another gene, but will also take bits and pieces from other genes and other species. Although this is aimed to benefit the expression and function of the "new" gene it also causes more interference and enhances the risks of unpredictable effects.
Yet there is a problem - a fish gene will not work in tomato unless I give it a promoter with a "flag" the tomato cells will recognise. Such a control sequence should either be a tomato sequence or something similar. Most companies and scientists do a shortcut here and don't even bother to look for an appropriate tomato promoter as it would take years to understand how the cell's internal communication and regulation works. In order to avoid long testing and adjusting, most genetic engineering of plants is done with viral promoters. Viruses - as you will be aware - are very active. Nothing, or almost nothing, will stop them once they have found a new victim or rather host. They integrate their genetic information into the DNA of a host cell (such as one of your own), multiply, infect the next cells and multiply. This is possible because viruses have evolved very powerful promoters which command the host cell to constantly read the viral genes and produce viral proteins. Simply by taking a control element (promoter) from a plant virus and sticking it in front of the information block of the fish gene, you can get this combined virus/fish gene (known as a "construct') to work wherever and whenever you want in a plant.
This might sound great, the drawback though is that it can't be stopped either, it can't be switched off. The plant no longer has a say in the expression of the new gene, even when the constant involuntary production of the "new" product is weakening the plant's defences or growth.
And furthermore, the theory doesn't hold up with reality. Often, for no apparent reason, the new gene only works for a limited amount of time and then "falls silent". But there is no way to know in advance if this will happen.
Though often hailed as a precise method, the final stage of placing the new gene into a receiving higher organism is rather crude, seriously lacking both precision and predictability. The "new" gene can end up anywhere, next to any
gene or even within another gene, disturbing its function or regulation. If the "new" gene gets into the "quiet" non-expressed areas of the cell's DNA, it is likely to interfere with the regulation of gene expression of the whole region. It could potentially cause genes in the "quiet" DNA to become active.
Often genetic engineering will not only use the information of one gene and put it behind the promoter of another gene, but will also take bits and pieces from other genes and other species. Although this is aimed to benefit the expression and function of the "new" gene it also causes more interference and enhances the risks of unpredictable effects.
What is Genetic Engineering?
We find it mixed in our food on the shelves in the supermarket--genetically engineered soybeans and maize. We find it growing in a plot down the lane, test field release sites with genetically engineered rape seed, sugar beet, wheat, potato, strawberries and more. There has been no warning and no consultation.
It is variously known as genetic engineering, genetic modification or genetic manipulation. All three terms mean the same thing, the reshuffling of genes usually from one species to another; existing examples include: from fish to tomato or from human to pig. Genetic engineering (GE) comes under the broad heading of biotechnology.
But how does it work? If you want to understand genetic engineering it is best to start with some basic biology.
What is a cell? A cell is the smallest living unit, the basic structural and functional unit of all living matter, whether that is a plant, an animal or a fungus.Some organisms such as amoebae, bacteria, some algae and fungi are single-celled - the entire organism is contained in just one cell. Humans are quite different and are made up of approximately 3 million cells -(3,000,000,000,000 cells). Cells can take many shapes depending on their function, but commonly they will look like a brick with rounded comers or an angular blob - a building block.Cells are stacked together to make up tissues, organs or structures (brain, liver, bones, skin, leaves, fruit etc.).
In an organism, cells depend on each other to perform various functions and tasks; some cells will produce enzymes, others will store sugars or fat; different cells again will build the skeleton or be in charge of communication like nerve cells; others are there for defence, such as white blood cells or stinging cells in jelly fish and plants. In order to be a fully functional part of the whole, most cells have got the same information and resources and the same basic equipment.
A cell belonging to higher organisms (e.g. plant or animal) is composed of:
• a cell MEMBRANE enclosing the whole cell. (Plant cells have an additional cell wall for structural reinforcement.)
• many ORGANELLES, which are functional components equivalent to the organs in the body of an animal e.g. for digestion, storage, excretion.
• a NUCLEUS, the command centre of the cell. It contains all the vital information needed by the cell or the whole organism to function, grow and reproduce. This information is stored in the form of a genetic code on the chromosomes, which are situated inside the nucleus.
Proteins are the basic building materials of a cell, made by the cell itself. Looking at them in close-up they consist of a chain of amino-acids, small specific building blocks that easily link up. Though the basic structure of proteins is linear, they are usually folded and folded again into complex structures. Different proteins have different functions. They can be transport molecules (e.g. oxygen binding haemoglobin of the red blood cells); they can be antibodies, messengers, enzymes (e.g. digestion enzymes) or hormones (e.g. growth hormones or insulin). Another group is the structural proteins that form boundaries and provide movement, elasticity and the ability to contract. Muscle fibres, for example, are mainly made of proteins. Proteins are thus crucial in the formation of cells and in giving cells the capacity to function properly.
Chromosomes means "coloured bodies" (they can be seen under the light microscope, using a particular stain). They look like bundled up knots and loops of a long thin thread. Chromosomes are the storage place for all genetic - that is hereditary - information. This information is written along the thin thread, called DNA. "DNA" is an abbreviation for deoxyribo nucleic acid, a specific acidic material that can be found in the nucleus. The genetic information is written in the form of a code, almost like a music tape. To ensure the thread and the information are stable and safe, a twisted double stranded thread is used - the famous double helix. When a cell multiplies it will also copy all the DNA and pass it on to the daughter cell.
The totality of the genetic information of an organism is called genome. Cells of humans, for example, possess two sets of 23 different chromosomes, one set from the mother and the other from -the father. The DNA of each human cell corresponds to 2 meters of DNA if it is stretched out and it is thus crucial to organise the DNA in chromosomes, so as to avoid knots, tangles and breakages. The length of DNA contained in the human body is approximately 60,000,000,000 kilometres. This is equivalent to the distance to the moon and back 8000 times!
The information contained on the chromo-somes in the DNA is written and coded in such a way that it can be understood by almost all living species on earth. It is thus termed the universal code of life. In this coding system, cells need only four symbols (called nucleotides) to spell out all the instructions of how to make any protein. Nucleotides are the units DNA is composed of and their individual names are commonly abbreviated to the letters A, C G and T These letters are arranged in 3-letter words which in turn code for a particular amino acid - as shown in the flow diagram 1. The information for how any cell is structured or how it functions is all encoded in single and distinct genes. A Gene is a certain segment (length) of DNA with specific instructions for the production of commonly one specific protein. The coding sequence of a gene is, on average about 1000 letters long. Genes code for example for insulin, digestive enzymes, blood clotting proteins, or pigments.
How does a cell know when to produce which protein and how much of it? In front of each gene there is a stretch of DNA that contains the regulatory elements for that specific gene, most of which is known as the promoter. It functions like a "control tower," constantly holding a "flag" up for the gene it controls. Take insulin production (which we produce to enable the burning of the blood sugar). When a message arrives in the form of a molecule that says, 'more insulin", the insulin control tower will signal the location of the insulin gene and say "over here". The message molecule will "dock in" and thus activate a "switch" to start the whole process of gene expression.
How does the information contained in the DNA get turned into a protein at the right time? As shown in picture 2, each gene consists of 3 main components: a "control tower" (promoter), an information block and a polyA signal element. If there is not enough of a specific protein present in the cell, a message will be sent into the nucleus to find the relevant gene. If the control tower recognises the message as valid it will open the "gate" to the information block. Immediately the information is copied - or transcribed - into a threadlike molecule, called RNA. RNA is very similar to DNA, except it is single stranded. After the copy is made, a string of up to 200 "A"-type nucleotides - a polyA tail - is added to its end (picture 2). This process is called poly-adenylation and is initiated by a polyA signal located towards the end of the gene. A polyA tail is thought to stabilise the RNA message against degradation for a limited time. Now the RNA copies of the gene leave the nucleus and get distributed within the cell to little work units that translate the information into proteins.
No cell will ever make use of all the information coded in its DNA. Cells divide the work up amongst one other - they specialise. Brain cells will not produce insulin, liver cells will not produce saliva, nor will skin cells start producing bone. If they did, our bodies could be chaos!
The same is true for plants: root cells will not produce the green chlorophyll, nor will the leaves produce pollen or nectar. Furthermore, expression is age dependent: young shoots will not express any genes to do with fruit ripening, while old people will not usually start developing another set of teeth (exceptions have been known).
All in all, gene regulation is very specific to the environment in which the cell finds itself and is also linked to the developmental stages of an organism. So f I want the leaves of poppy plants to produce the red colour of the flower petals I will not be able to do so by traditional breeding methods, despite the fact that leaf ells will have all the genetic information necessary. There is a block that prevents he leaves from going red. This block may be caused by two things:
• The "red" gene has been permanently shut down and bundled up thoroughly in all leaf cells. Thus the information cannot be accessed any more.
• The leaf cells do not need the colour red and thus do not request RNA copies of this information. Therefore no message molecule is docking at the "red" control tower to activate the gene.
Of course - you might have guessed - there is a trick to fool the plant and make it turn red against its own will. We can bring the red gene in like a Trojan horse, hidden behind the control tower of a different gene. But for this we need to cut the genes up and glue them together in a different form. This is where breeding ends and genetic engineering begins.
BREEDING is the natural process of sexual reproduction within the same species. The hereditary information of both parents is combined and passed on to the offspring. In this process the same sections of DNA can be exchanged between the same chromosomes, but genes will always remain at their very own and precise position and order on the chromosomes. A gene will thus always be surrounded by the same DNA unless mutations or accidents occur. Species that are closely related might be able to interbreed, like a donkey and a horse, but their offspring will usually be infertile (e.g. mule). This is a natural safety devise, preventing the mixing of genes that might not be compatible and to secure the survival of the species.
It is variously known as genetic engineering, genetic modification or genetic manipulation. All three terms mean the same thing, the reshuffling of genes usually from one species to another; existing examples include: from fish to tomato or from human to pig. Genetic engineering (GE) comes under the broad heading of biotechnology.
But how does it work? If you want to understand genetic engineering it is best to start with some basic biology.
What is a cell? A cell is the smallest living unit, the basic structural and functional unit of all living matter, whether that is a plant, an animal or a fungus.Some organisms such as amoebae, bacteria, some algae and fungi are single-celled - the entire organism is contained in just one cell. Humans are quite different and are made up of approximately 3 million cells -(3,000,000,000,000 cells). Cells can take many shapes depending on their function, but commonly they will look like a brick with rounded comers or an angular blob - a building block.Cells are stacked together to make up tissues, organs or structures (brain, liver, bones, skin, leaves, fruit etc.).
In an organism, cells depend on each other to perform various functions and tasks; some cells will produce enzymes, others will store sugars or fat; different cells again will build the skeleton or be in charge of communication like nerve cells; others are there for defence, such as white blood cells or stinging cells in jelly fish and plants. In order to be a fully functional part of the whole, most cells have got the same information and resources and the same basic equipment.
A cell belonging to higher organisms (e.g. plant or animal) is composed of:
• a cell MEMBRANE enclosing the whole cell. (Plant cells have an additional cell wall for structural reinforcement.)
• many ORGANELLES, which are functional components equivalent to the organs in the body of an animal e.g. for digestion, storage, excretion.
• a NUCLEUS, the command centre of the cell. It contains all the vital information needed by the cell or the whole organism to function, grow and reproduce. This information is stored in the form of a genetic code on the chromosomes, which are situated inside the nucleus.
Proteins are the basic building materials of a cell, made by the cell itself. Looking at them in close-up they consist of a chain of amino-acids, small specific building blocks that easily link up. Though the basic structure of proteins is linear, they are usually folded and folded again into complex structures. Different proteins have different functions. They can be transport molecules (e.g. oxygen binding haemoglobin of the red blood cells); they can be antibodies, messengers, enzymes (e.g. digestion enzymes) or hormones (e.g. growth hormones or insulin). Another group is the structural proteins that form boundaries and provide movement, elasticity and the ability to contract. Muscle fibres, for example, are mainly made of proteins. Proteins are thus crucial in the formation of cells and in giving cells the capacity to function properly.
Chromosomes means "coloured bodies" (they can be seen under the light microscope, using a particular stain). They look like bundled up knots and loops of a long thin thread. Chromosomes are the storage place for all genetic - that is hereditary - information. This information is written along the thin thread, called DNA. "DNA" is an abbreviation for deoxyribo nucleic acid, a specific acidic material that can be found in the nucleus. The genetic information is written in the form of a code, almost like a music tape. To ensure the thread and the information are stable and safe, a twisted double stranded thread is used - the famous double helix. When a cell multiplies it will also copy all the DNA and pass it on to the daughter cell.
The totality of the genetic information of an organism is called genome. Cells of humans, for example, possess two sets of 23 different chromosomes, one set from the mother and the other from -the father. The DNA of each human cell corresponds to 2 meters of DNA if it is stretched out and it is thus crucial to organise the DNA in chromosomes, so as to avoid knots, tangles and breakages. The length of DNA contained in the human body is approximately 60,000,000,000 kilometres. This is equivalent to the distance to the moon and back 8000 times!
The information contained on the chromo-somes in the DNA is written and coded in such a way that it can be understood by almost all living species on earth. It is thus termed the universal code of life. In this coding system, cells need only four symbols (called nucleotides) to spell out all the instructions of how to make any protein. Nucleotides are the units DNA is composed of and their individual names are commonly abbreviated to the letters A, C G and T These letters are arranged in 3-letter words which in turn code for a particular amino acid - as shown in the flow diagram 1. The information for how any cell is structured or how it functions is all encoded in single and distinct genes. A Gene is a certain segment (length) of DNA with specific instructions for the production of commonly one specific protein. The coding sequence of a gene is, on average about 1000 letters long. Genes code for example for insulin, digestive enzymes, blood clotting proteins, or pigments.
How does a cell know when to produce which protein and how much of it? In front of each gene there is a stretch of DNA that contains the regulatory elements for that specific gene, most of which is known as the promoter. It functions like a "control tower," constantly holding a "flag" up for the gene it controls. Take insulin production (which we produce to enable the burning of the blood sugar). When a message arrives in the form of a molecule that says, 'more insulin", the insulin control tower will signal the location of the insulin gene and say "over here". The message molecule will "dock in" and thus activate a "switch" to start the whole process of gene expression.
How does the information contained in the DNA get turned into a protein at the right time? As shown in picture 2, each gene consists of 3 main components: a "control tower" (promoter), an information block and a polyA signal element. If there is not enough of a specific protein present in the cell, a message will be sent into the nucleus to find the relevant gene. If the control tower recognises the message as valid it will open the "gate" to the information block. Immediately the information is copied - or transcribed - into a threadlike molecule, called RNA. RNA is very similar to DNA, except it is single stranded. After the copy is made, a string of up to 200 "A"-type nucleotides - a polyA tail - is added to its end (picture 2). This process is called poly-adenylation and is initiated by a polyA signal located towards the end of the gene. A polyA tail is thought to stabilise the RNA message against degradation for a limited time. Now the RNA copies of the gene leave the nucleus and get distributed within the cell to little work units that translate the information into proteins.
No cell will ever make use of all the information coded in its DNA. Cells divide the work up amongst one other - they specialise. Brain cells will not produce insulin, liver cells will not produce saliva, nor will skin cells start producing bone. If they did, our bodies could be chaos!
The same is true for plants: root cells will not produce the green chlorophyll, nor will the leaves produce pollen or nectar. Furthermore, expression is age dependent: young shoots will not express any genes to do with fruit ripening, while old people will not usually start developing another set of teeth (exceptions have been known).
All in all, gene regulation is very specific to the environment in which the cell finds itself and is also linked to the developmental stages of an organism. So f I want the leaves of poppy plants to produce the red colour of the flower petals I will not be able to do so by traditional breeding methods, despite the fact that leaf ells will have all the genetic information necessary. There is a block that prevents he leaves from going red. This block may be caused by two things:
• The "red" gene has been permanently shut down and bundled up thoroughly in all leaf cells. Thus the information cannot be accessed any more.
• The leaf cells do not need the colour red and thus do not request RNA copies of this information. Therefore no message molecule is docking at the "red" control tower to activate the gene.
Of course - you might have guessed - there is a trick to fool the plant and make it turn red against its own will. We can bring the red gene in like a Trojan horse, hidden behind the control tower of a different gene. But for this we need to cut the genes up and glue them together in a different form. This is where breeding ends and genetic engineering begins.
BREEDING is the natural process of sexual reproduction within the same species. The hereditary information of both parents is combined and passed on to the offspring. In this process the same sections of DNA can be exchanged between the same chromosomes, but genes will always remain at their very own and precise position and order on the chromosomes. A gene will thus always be surrounded by the same DNA unless mutations or accidents occur. Species that are closely related might be able to interbreed, like a donkey and a horse, but their offspring will usually be infertile (e.g. mule). This is a natural safety devise, preventing the mixing of genes that might not be compatible and to secure the survival of the species.
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